A signal transmission system based on the DVI (Digital Visual Interface) standard, which is one of conventional digital signal transmission methods, will be described with reference to FIG. 25. FIG. 25 is a diagram illustrating the construction for realizing a serial transfer system referred to as TMDS (Transition Minimized Differential Signaling), which is one of the conventional transmission systems.
In the drawing, numerals 2601˜2603 denote TMDS encoders/serializers which are provided in a signal transmission apparatus. The TMDS encoders/serializers 2601˜2603 perform TMDS encoding on inputted component signals such as RED, GREEN, and BLUE, serialize the encoded component signals, and output the serialized component signals to a transmission path. Numerals 2604˜2606 denote TMDS decoders/recovery units which are provided in a signal reception apparatus. The TMDS decoders/recovery units 2604˜2606 perform TMDS decoding on the received signals and recover the decoded signals, thereby reconstructing the component signals. A DE (Data Enable) signal indicates a period during which a component signal such as RED, GREEN, or BLUE exists, and this is a HIGH active signal. For example, a period during which the DE signal is LOW is a horizontal sync signal period or vertical sync signal period of video. CTL (control) signals, CTL0, CTL1, CTL2, and CTL3, are prepared as control signals. However, in the current DVI standard, the CTL signals CTL1, CTL2, and CTL3 are not used yet. To be specific, the levels of the control signals are “0” at all time.
The conventional signal transmission system so constructed will be described.
In each of the TMDS encoders/serializers 2601˜2603 in the signal transmission apparatus, a video signal (RGB signal) inputted at 8 bits is converted into a 10-bit video signal, and it is serialized to be outputted to the transmission path. The 8-bits/10-bits conversion aims to reduce the number of change points of data so as to convert the video signal into a form suited for high-speed transmission. Further, in the TMDS encoders/serializers 2601˜2603, a 2-bit CTL signal is converted into a 10-bit CTL signal to be outputted to the transmission path. Further, the DE signal is also encoded, serialized, and outputted to the transmission path.
In each of the TMDS decoders/recovery units 2604˜2606 in the signal reception apparatus, the 10-bit serial data received through the transmission path is decoded and recovered to the 8-bit chrominance signal, the DE signal, and the 2-bit CTL signal.
However, the DVI standard is a standard for transmitting only video signals (RGB signals), and therefore, the conventional signal transmission system based on the DVI standard cannot transmit an audio signal and a control signal for controlling a monitor. The signal for controlling the monitor is a control signal to realize a processing in a device to be connected, utilizing features of the signal. Hereinafter, the signal for controlling the monitor is referred to simply as a control signal.
That is, conventionally, an audio signal is transmitted through a different line and, thus, cable connection between the signal transmission apparatus and the signal reception apparatus is extremely complicated for a user. Further, the audio signal is not under copy protection. Furthermore, the control signal cannot be transmitted in the current analog connection and can be transmitted only as an auxiliary signal of video in a vertical blanking period (VBK), and since the control signal has a narrow band, advanced processing cannot be carried out, resulting in frequent errors.
The present invention is made to solve the above-described problems and has for its object to provide a signal transmission apparatus and a signal reception apparatus, which realize a signal transmission system that is applied to the DVI standard, and capable of transmitting an audio signal and a control signal for controlling a monitor, together with a video signal.